diy solar

diy solar

AC coupled battery supplying essential sub panel with Grid tied Micro inverter - Wiring question

Thanks for the clear explanation, I understood now.
For this back feed, how do you calculate the breaker size? If your inverter can do grid forming, would that not make the maximum current your PV current + battery inverter max current?

It sounds like rewiring to make space on main panel is not avoidable..
 
Yes, the backfed breaker ("generator" input to main panel) could carry as much as PV inverter current + battery inverter current.
But you do have loads on your protected loads panel as well, which could be consuming some of the available power.
I have a 100A breaker in that position (connected with 2 awg). The breaker going to my house is 70 awg for now because wire is 6 awg, plan to pull larger wire eventually.
Often this circuit would be wired as 30A for a generator. It's up to you to limit the loads connected.

You obviously need at least one 2-pole position at end of the main panel for your PV breaker. One more by the main breaker if you want to backfeed when grid is down. I was starting with an empty 40 position panel I put in for the project, but if yours is full you could use tandem breakers, put pairs of circuits on a single breaker, or move circuits to a downstream panel.

Are you familiar with wiring that has a cable with two hots (red, black) on different phases feeding two circuits but sharing a neutral? If panel has those you need to keep them on separate phases when rewiring the panel.

My battery inverter (Sunny Island) does not connect to grid when first powered on. It powers loads from battery for 5 minutes while monitoring grid, then synchronizes frequency, then connects. If battery gets drained to the point of shutting down, it can't charge from either grid or AC coupled PV. Do you know if your planned battery inverter behaves that way, or if it will just close relay and let grid power through?

Having DC coupled PV is one way to recharge battery even if Sunny Island is shut down. For mine, I have a "load shed" relay which disconnects the house at 70% DoD. That way it can still power the protected loads panel, which has only AC coupled PV, so charging can resume. Once I've separately wired more branches, a second load shed relay will disconnect garage circuit (the backfed one) at 20% DoD. I will also wire control signals to A/C thermostat so it disconnects before battery is significantly discharged; it is meant to just run when PV is available.
 
Got it.
I have a 10 space 100A mbp + meter combined unit. I had to do a like-like replace from the original 1970 model to a solar ready ( 125A bus bar ) panel. When the inspector came he did nag the electrician about the 4 wire romex not connecting on alternated phase problem, so I understand what the AB phase issue is about. ( It really do sounds like a minute detail though.. Even if I have it wired to A/B phase, but if I somehow switched on the right appliance, and only draw power from all of the A phase, the imbalance will still happen isn't it? )

It sounds like I have to make space on the main panel anyway then. Maybe I can just get a few more circuit to the sub panel, so I don't even need to backfeed to main panel with another #2 cable, and put interlock on the surge panel to ensure it does not back feed to mbp this way.

More planning and thinking to do.. Thanks a lot for sharing your experience to help me form the plan!
 
Far from a minute detail. Romex 3 + ground has 20 awg black, red, white, bare. If 20A drawn on black and red fed by opposite phases, white carries zero. If 20A on black and zero on red, white carries 20A.
But if black and red each wired to 20A breakers on the same phase, each carrying 20A doesn't trip breaker but white carries 40A and overheats.

Having the option of backfeed is convenient if it turns out the crawl space light or garage door opener is on main panel. I didn't like the $50 price for a piece of sheetmetal but I finally broke down and bought it.

If you have ordinary single phase breakers in single slots, you can probably put in tandem and combine two (from the same phase) into one breaker body with two breakers inside. But if they are GFCI or AFCI, I'm not aware of tandem versions of those. I was also able to get 20/30 and 30/20 tandem breakers, also tie bars, so a 2 pole 30A could take up less space.
 
Opps. Shows that I don't know what the AB rule actually means. Thanks for clearing it up for me.

Will look into tandem breaker. I never imagine I will be drawing a diagram for my power panel, but I might need to do it to properly plan this.

Again, thanks for sharing the experience!
 
newbostonconst said:
Some on here have the newer Skybox but I don't know the advantage to that.
Click to expand...
I have a Skybox and the only advantage is that it was designed to be grid interactive. I have great respect fot Outback products and previously owned a Radian GS4048. The Radian has better surge capacity and comes in 4 kW and 8 KW versions.
 
mufasa said:
Found this post discussing pro and con about skybox vs radian.
Click to expand...
I don't know how I missed that thread. I spend time on that forum but mostly on the Skybox section. There were some misconceptions. The most that the Skybox can invert is 5kW but you can add AC coupled solar for an additional 7kW of energy. That gives you close to 12 kW which you could backfeed to the grid. Your 6.4 kW of solar is probably only 5kW in terms of total microinverter capacity anyway. What size micros and hiw many d you have? As @400bird points out earlier that is 48 Amps continious or 11.5 kW.
The Skybox also has more grid interactive modes and is an all in one. You don't need a separate charge controller or other devices. For your purposes it would be less expensive. They are wired the same. Did you get your question answered in that regard?
 
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As ampster stated....do you have all your questions answered?

I had planed to add the blade device Hedges mentioned to interlock the Inverter and main disconnect breakers to prevent them both from being on at the same time but they don't have one for my panel and it stops me from back feeding to my main panel if I want the inverter to power the whole house. I made my phases match so back feeding isn't a problem for me if the breakers are tripped in the wrong order. If in total backup and back feeding the whole house the grid side breaker feeding the inverter has to be off or the inverter will not control the micros correctly in AC coupling mode. It will just keep shutting the micros down by frequency shifting but work fine other then that.

I am getting ready to add another 7k of solar to the house for more EV charging and to switch the house over to more electric and get rid of Natural Gas heating. I will likely add the solar through DC coupling with a Outback FM100 solar charge controller. Once I do this the house will be run in grid zero mode unless batteries are ran down and the inverter changes back to grid. These functions are still supposed to work. There are a couple functions in the GS manual that can't run at the same time but it is logical in the manual..... The manual is very thorough but complex, plan to read it a couple times. Download it now....The GS manual covers all components that can be connected to it, so if you don't have that component (like a solar charge controller) ignore that section. They was very confusing to me till I figured that out. Same in the MATE3, everything is listed but you will only use the inverter section unless you have a solar charge controller or something else connected. They should have grayed out the stuff not in use but they didn't.

Being you already have Micros the Outback GS is the cheapest way to go but there are other options. Good Luck.
 
As far as I know, there are only two solutions:
  1. AC Coupling, which has been discussed with products like the Skybox.
  2. AC Battery capable of managing the microinverters, of which there are two solutions: Enphase Ensemble and Tesla's Powerwall for solar. Both are complete solutions that include the ATS and other components. Tesla looks cheaper on the surface, although I've heard when folks get the estimates it's about on par with Ensemble.
I can't speak to Tesla, but have blogged my experiences with Ensemble.
 
svetz said:
As far as I know, there are only two solutions:
  1. AC Coupling, which has been discussed with products like the Skybox.
  2. AC Battery capable of managing the microinverters, of which there are two solutions: Enphase Ensemble and Tesla's Powerwall for solar. .
Click to expand...


I'm sure you know this, but I feel the need to clarify if someone comes across this post and I'd unsure.
There are no AC batteries. It just isn't possible.

Both the Tesla power wall and Enphase Ensemble are DC batteries with inverters integrated in the same housing.

So the two basic options you list (AC couple or AC battery) looks to me like DIY or buy.
 
newbostonconst said:
I had planed to add the blade device Hedges mentioned to interlock the Inverter and main disconnect breakers to prevent them both from being on at the same time but they don't have one for my panel and it stops me from back feeding to my main panel if I want the inverter to power the whole house.
Click to expand...

Something like Reliance transfer switch would be a way to backfeed half a dozen circuits. It has SPDT and DPDT switches so those circuits are fed either from the original single (or double) breaker in main panel, or from a breaker in Reliance which is powered by inverter. Only for normal breakers, not AFCI or GFCI because those require neutral wire switched as well. I think I figured out how single phase circuits of those types could work, rewiring one of the DPDT switches.

Given a protected loads panel, just SPDT, DPDT, even 3PDT switches could implement the same function as reliance. But it is UL listed, and use of just switches (even same ones) would probably not qualify. I know my utility wanted a visible-blade switch to isolate inverter from grid. Any toggle switch would replace that visible several inch gap without about 1/10th of an inch gap inside the switch. it's failure closed on both sides would connect inverter to grid. (If that's what is used inside Reliance I can't see how it is better, just "listed".)
 
svetz said:
As far as I know, there are only two solutions:
  1. AC Coupling, which has been discussed with products like the Skybox.
  2. AC Battery capable of managing the microinverters, of which there are two solutions: Enphase Ensemble and Tesla's Powerwall for solar. Both are complete solutions that include the ATS and other components. Tesla looks cheaper on the surface, although I've heard when folks get the estimates it's about on par with Ensemble.
I can't speak to Tesla, but have blogged my experiences with Ensemble.
Click to expand...
Not sure how you are saying there are only 2 solutions: Two solutions that fit the OP's situation? Two AC coupling solutions? Two with transfer switches?
 
Since the OP has micros the only practical solutions to adding backup are AC coupling. If he wants to throw away the micros and DC couple the solar panels to a hybrid inverter then that is another solution but in my mind, not a practical one. Some people refer to the Tesla Powerwall and the Enphase Ensemble as AC batteries, but they are just an inverter and battery integrated into a packgage that can AC couple.
 
Ampster said:
Since the OP has micros the only practical solutions to adding backup are AC coupling. If he wants to throw away the micros and DC couple the solar panels to a hybrid inverter then that is another solution but in my mind, not a practical one. Some people refer to the Tesla Powerwall and the Enphase Ensemble as AC batteries, but they are just an inverter and battery integrated into a packgage that can AC couple.
Click to expand...
But are not DIY that I know of. Outback, SolArk, and Schneider are the only ones I know of......Just saw a cheap Phocos that doesn't AC couple though.
 
newbostonconst said:
But are not DIY that I know of. Outback, SolArk, and Schneider are the only ones I know of......Just saw a cheap Phocos that doesn't AC couple though.
Click to expand...

Also SMA Sunny Boy Storage (uses 400V lithium, similar function to PowerWall) or Sunny Island (48V, variety of chemistries).
I don't know if anyone does 400V DIY batteries. Using 280 Ah cells, would be about 115kW. The commercial ones are made of smaller cells for 3 kW to 30 kW. Some (LG RESU) require an approved installer to get warranty, but that is just an on-line training and test.
The 48V batteries of course can be DIY.

Pricewise, you can get two Sunny Island (for 120/240V) for about $4k to $5k. A single one will work for up to 6.7kW of PV but you need a 120/240V transformer. Not cheap, but not a bad price. Good if you have heavy motor loads to start. Powerwall, for instance, has anemic surge and is getting some increased performance in a new model, but would still be limited. I would guess < 2000W of motor. If no such motor loads, then the high-frequency battery inverters are also an option.

If the microinverters do frequency-watts, any of these AC coupled battery inverters that do frequency shift should be good.
If the inverters don't curtail output, they're going to get cycled on/off and battery will repeatedly charge/discharge about 5 minutes on and off.

The "AC batteries" are often marketed as working with any GT inverter. Not sure if they're counting on recent installations which do frequency-watts. Probably quite a few UL-1741SA that simply ride through for 5 minutes at 100% output, which might help the grid but doesn't do anything to match battery current acceptance. I think the batteries just cycle up and down. If you have 5kW PV and 2500W load, it charges at 2500W for 5 minutes, knocks inverters off-line, discharges at 2500W for 5 minutes, then repeats. The off-line discharge ramp is always 5 minutes, the on-line charge ramp depends on ratio of PV watts to load.

When operating off-grid, frequency shift can be used to control production. The on-grid zero-export systems would use communication (possibly just a relay to pull the plug) which knocks GT inverters off-line whenever battery can't absorb enough to prevent export. Or, communication to throttle back production.

This product for Sunny Boy Storage (200A transfer switch, 120/240V transformer, current transformers) appears to take care of zero export as well as backup operation:


This one controls PV inverters (of same SMA brand) for zero export:

 
Hedges said:
The "AC batteries" are often marketed as working with any GT inverter. Not sure if they're counting on recent installations which do frequency-watts.
Click to expand...
I think "frequency-watts" has been around since the UL 1741 spec was originally adopted. Are you referring to UL 1741SA which includes modulation by frequency-watts?
 
Ampster said:
I think "frequency-watts" has been around since the UL 1741 spec was originally adopted. Are you referring to UL 1741SA which includes modulation by frequency-watts?
Click to expand...

I didn't know frequency-watts (ramp down of wattage for a range of increasing frequency) was part of original UL 1741. I've only seen some details in presentations explaining UL 1741SA. It seems to be just like what SMA implemented for off-grid operation, except maybe frequencies where it occurs are different from the default setting in SMA.

It appears to me frequency-watts is an optional implementation which can only be used with utility's permission.
I think an inverter is only required to implement the 299 second ride-through/300 second disconnect for frequency and voltage out of spec by a limited amount to comply with UL 1741SA.

GT PV inverters that implement frequency/watts "modulation" (or linear curtailment) of power output should play nice with battery inverters that do frequency shift. Assuming reliable bug-free firmware, which it appears not all GT PV inverters have.
 
Wow so many replies! I am glad I asked the question. Thanks for all the answer and discussion, I learned a lot.

Yes I have all of my question answered, and then some.

My 16 micro is enphase iq7A, it seems to be supporting UL1741SA. That is enabled by specifying the "CA Rule21 201902 VV VW FW" profile right? ( forgot where I read about that )

I did get some quotes for powerwall / enpower, and they are.. pricy. I just DIY my own PV system, trying to save on the cost, so I also plan to find battery solution that would allow DIY route.

Right now I am leaning toward outback skybox. The all in one option does give a lot of appeal, and the fact that it allows connecting PV panel directly as a dc inverter is also nice - Maybe when I get to the time of expand PV installation, I can just hook a few more panel onto outback to help charge battery and also supply the house.

So right now my plan goes like this:

Code: 
Main panel ===== surge load panel === outback === essential panel === PV
                         |======== pass through ========|
                         |== Future EV charger
                         |== Table saw

I will move several circuit to the essential panel, including most of the interior light, a few kitchen appliance plugs, network / PC / security cameras and fridge / freezer.

The surge load panel should have a interlock so the main-> surge load panel breaker and the passthrough / backfead breaker can't be switched on at the same time. So even if I enable that backfeed, at most I power the surge load panel. ( maybe I should move the soon to be installed heatpump to that surge panel ? decision decision.. )
Basically I gave up on backfeeding to the main panel, and try to move all circuit I need battery backup to the essential panel.

Battery choice likely will be the DIY Li-Fe 48V batteries.

Hopefully the plan looks right now. If anything that still looks out of place, please don't hesitate to point out!
 
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